1. Field of the Invention
The present invention relates to apparatus for treating clays such as kaolin for the purpose of brightening the clay to render it more valuable and more particularly relates to froth flotation apparatus and method for treating aqueous clay slurries to remove titanium mineral impurities therefrom.
2. Prior Art
Froth flotation has been employed for decades for the purpose of removing impurities from ores and clays. A wide variety of flotation machines utilize violent agitation for the purpose of sucking air in from the atmosphere and distributing it throughout the pulp. The Denver Sub-A cell, the Fagergren flotation machine and the Agitair flotation machine typify this type of flotation equipment. These include an impeller located in the bottom, a pipe extending from the impeller upwardly to the atmosphere above the liquid level in the cell such that when the impeller rotates a suction is created for pulling air down through the pipe to the impeller which then distributes it in the form of bubbles throughout the pulp contained in the cell. Apparatus of this type cannot be utilized in a generally quiescent mode but depends upon the violent action of the impeller for bubble entrainment.
Illustrations of flotation apparatus in which air is introduced into the bottom of the cell without the use of a violent agitation caused by an impeller are given in U.S. Pat. Nos. 3,525,437, 3,730,341 and 4,287,054. In each of these illustrations however, diluting water containing entrained air bubbles is utilized to introduce air bubbles into the cell. Furthermore, none of these patents disclose the recycling of an unfloated fraction or the use of a recycled portion for carrying air bubbles into the pulp in the cell.
U.S. Pat. No. 3,701,421 utilizes an impeller 20 for agitating the pulp in a flotation cell and introduces air into the cell under the impeller so that the air is distributed by the impeller throughout the pulp. There is no disclosure or suggestion of recycling unfloated fractions removed from the lower portion of the cell and entraining air bubbles in the recycle portion.
The Steffensen flotation machine is extensively used and comprises an inverted cone-shaped cell into which the pulp is fed and into the narrow portion of which air is blown. U.S. Pat. No. 1,646,019 passes pulp through a trough into the bottom of which air is blown which forms a froth on the top of the pulp. The pulp travels in a generally horizontal direction while the air is being blown through it to provide a cross current type of flow rather than counter current flow. In addition, the apparatus of this patent and the Steffensen flotation apparatus fail to recycle an unfloated portion of the pulp after entraining air into said portion.